docs: def last_modified(self) -> str:
  		"""
  		Return an ISO8601 timestamp indicating when the file was last modified
  
  		Returns:
  			An ISO8601 timestamp indicating when the file was last modified
  
  		Remarks:
  			If the file has no timestamp, and mode is 'r+', a new timestamp is created and returned.
  			Otherwise, the current time in UTC is returned
  		"""
  		if "last_modified" in self.attrs:
  			return self.attrs["last_modified"]
  		elif self.mode == "r+":
  			# Make sure the file has modification timestamps
  			self.attrs["last_modified"] = timestamp()
  			return self.attrs["last_modified"]
  		return timestamp()